Driving device, air conditioner, and method for driving motor

Abstract

A driving device drives a motor having coils. The driving device includes a converter to generate a bus voltage, an inverter to convert the bus voltage to an AC voltage and supply the AC voltage to the coils, and a connection switching unit to switch a connection state of the coils. The bus voltage generated by the converter is switched in accordance with the connection state of the coils.

What is claimed is: 
     
       1. A driving device to drive a motor having coils, the driving device comprising:
 a converter to generate a bus voltage; 
 an inverter to convert the bus voltage to an AC voltage and supply the AC voltage to the coils; and 
 a connection switching device to switch a connection state of the coils; 
 wherein the connection state of the coils has a first connection state and a second connection state; 
 wherein a line voltage in the coils is lower in the second connection state than in the first connection state for a same rotation speed of the motor; and 
 wherein in a case where the connection switching device switches the connection state of the coils from the first connection state to the second connection state, the bus voltage generated by the converter is switched from a first bus voltage V1 to a second bus voltage V2 higher than the first bus voltage V1. 
 
     
     
       2. The driving device according to  claim 1 , wherein in a case where the connection switching device switches the connection state of the coils from the first connection state to the second connection state, rotation of the motor is stopped temporarily, and the connection switching device switches the connection state of the coils from the first connection state to the second connection state while the motor is stopped. 
     
     
       3. The driving device according to  claim 1 , wherein the coils are three-phase coils, and
 wherein the first connection state is a state where the three-phase coils are connected in a Y connection, and the second connection state is a state where the three-phase coils are connected in a delta connection. 
 
     
     
       4. The driving device according to  claim 3 , wherein a first rotation speed N1 and a second rotation speed N2 of the motor satisfy N2/N1>√3;
 wherein in a case where a rotation speed of the motor is the first rotation speed N1, the connection switching device sets the connection state of the coils to the first connection state; and 
 wherein in a case where the rotation speed of the motor is the second rotation speed N2, the connection switching device sets the connection state of the coils to the second connection state. 
 
     
     
       5. The driving device according to  claim 4 , wherein the first bus voltage V1, the second bus voltage V2, the first rotation speed N1 and the second rotation speed N2 satisfy V2≥(V1/√3)×N2/N1. 
     
     
       6. The driving device according to  claim 1 , wherein the coils are three-phase coils connected in a Y connection or a delta connection,
 wherein the first connection state is a state where the three-phase coils have serially-connected coil portions in a first number for each phase, and 
 wherein the second connection state is a state where the three-phase coils have parallely-connected coil portions in the first number for each phase. 
 
     
     
       7. The driving device according to  claim 6 , wherein the first number is expressed as “n”;
 wherein a first rotation speed N1 and a second rotation speed N2 of the motor satisfy N2/N1>n; 
 wherein in a case where a rotation speed of the motor is the first rotation speed N1, the connection switching device sets the connection state of the coils to the first connection state; and 
 wherein in a case where the rotation speed of the motor is the second rotation speed N2, the connection switching device sets the connection state of the coils to the second connection state. 
 
     
     
       8. The driving device according to  claim 7 , wherein the first bus voltage V1, the second bus voltage V2, the first rotation speed N1 and the second rotation speed N2 satisfy
     V 2≥( V 1/ n )× N 2/ N 1.
 
 
     
     
       9. The driving device according to  claim 4 , wherein the motor is used in an air conditioner;
 wherein the first rotation speed N1 corresponds to an intermediate heating condition for the air conditioner; and 
 wherein the second rotation speed N2 corresponds to a rated heating condition for the air conditioner. 
 
     
     
       10. The driving device according to  claim 4 , wherein the motor is used in an air conditioner;
 wherein the first rotation speed N1 corresponds to a condition that yields a highest ratio in an annual performance factor (APF) for the air conditioner; 
 wherein the second rotation speed N2 corresponds to a condition that yields a second highest ratio in the annual performance factor for the air conditioner. 
 
     
     
       11. The driving device according to  claim 1 , further comprising a power source to supply an AC power supply voltage to the converter;
 wherein the first bus voltage V1 is the same as √2 times an effective value of the power supply voltage. 
 
     
     
       12. The driving device according to  claim 1 , wherein the connection switching device switches the connection state of the motor to the first connection state in a case where a rotation speed of the motor is less than or equal to a threshold, and switches the connection state of the motor to the second connection state in a case where the rotation speed of the motor is greater than the threshold. 
     
     
       13. The driving device according to  claim 1 , wherein the inverter performs field-weakening control in accordance with a rotation speed of the motor. 
     
     
       14. The driving device according to  claim 1 , wherein the converter has a SiC element or a GaN element. 
     
     
       15. An air conditioner comprising:
 a motor having coils; 
 a compressor driven by the motor; and 
 a driving device to drive the motor, 
 wherein the driving device comprises: 
 a converter to generate a bus voltage; 
 an inverter to convert the bus voltage to an AC voltage and supply the AC voltage to the coils; and 
 a connection switching device to switch a connection state of the coils, 
 wherein the connection state of the coils has a first connection state and a second connection state; 
 wherein a line voltage in the coils is lower in the second connection state than in the first connection state for a same rotation speed of the motor; and 
 wherein in a case where the connection switching device switches the connection state of the coils from the first connection state to the second connection state, the bus voltage generated by the converter is switched from a first bus voltage V1 to a second bus voltage V2 higher than the first bus voltage V1. 
 
     
     
       16. A method for driving a motor having coils, the method using a converter to generate a bus voltage and an inverter to convert the bus voltage to an AC voltage and supply the AC voltage to the coils,
 wherein the connection state of the coils has a first connection state and a second connection state, and a line voltage in the coils is lower in the second connection state than in the first connection state for a same rotation speed of the motor, 
 the method comprising the steps of: 
 switching the connection state of the coils from the first connection state to the second connection state, and 
 switching the bus voltage generated by the converter from a first bus voltage V1 to a second bus voltage V2 higher than the first bus voltage V1 in a case where the connection state of the coils is switched from the first connection state to the second connection state.